Allow alternative wait action inside in a multiple wait action

[SasinduDilshara]

Description:

Consider the following code.

import ballerina/log;

type WaitResult record {|
    boolean|error producer;
    boolean consumer;
|};

public function main() {
    log:printInfo("initializing app...");

    // Producer 1
    worker Producer1 returns boolean|error {
        int i = 100;
        i -> Consumer;
        error? unionResult = flush Consumer;
        log:printInfo("Sent item", i = i);
        return true;
    }

    worker Producer2 returns boolean|error {
        int i = 100;
        i -> Consumer;
        error? unionResult = flush Consumer;
        log:printInfo("Sent item", i = i);
        return true;
    }

    // Consumer
    worker Consumer returns boolean {
        int i = <- Producer;
        log:printInfo("Received item", i = i);
        return false;
    }

    WaitResult res = wait {producer: Producer1|Producer2, consumer: Consumer};
    log:printInfo("Worker execution finished", result = res);
}

Do we allow following code to run without compiler error?
WaitResult res = wait {producer: Producer1|Producer2, consumer: Consumer};

Related Issues:

ballerina-platform/ballerina-lang#34821

[SasinduDilshara]

As I understood, currently the Ballerina spec support only for future<T> or in-scope worker-name in a variable-reference-expr to refer to named worker inside the multiple wait actions.
But I think we need to add support for alternative wait actions inside the multiple wait statements.

WDYT?

[jclark]

I think the spec is clear that this is not allowed.

I guess the spec could be enhanced to allow this. Probably, one would want to allow nesting of alternative and multiple waits in a general way.

Unless this is something we are finding that real users need, I would not give this a high priority.

[sanjiva]

Being able to wait for k out of n workers (which are in an array) to complete is very useful. Simplest case is to make concurrent calls to 2 services and take the first result.